This invention is directed to an anti-theft device consisting of a nut which screws onto the hub bolt of an automobile, and a turning device or key which matches the configuration of the lug nut. However, the lug nut must have a specific configuration in order to have no one, other than a specific individual, such as the owner, to turn it with the matching key in his possession. To achieve this, the lug nut and its matching, or complementary, turning device or key must be designed so as to be made with a plurality of configurations which can be readily changed, so that each automobile in a given geographical area can be equipped with a different lug nut and key device.
In the past, in anti-theft devices of the type described, there were devices with a multiple of protrusions having a semi-circular cross-section on the forward portion of the perimeter surface of a nut with a semi-spherical head (refer to Japanese Application Ser. No. 57-194918 ) or a nut with continuous protrusions with a polygonal cross-section along the perimeter with varying pitch, and in additon, with broken mounds (refer to Japanese Application Ser. No. 54-131657). But in these types of configurations of the nut, even when the configurations are changed, the number is limited due to the fact that the former only has a multiude of protrusions, and the latter only has continuous protrusion or mound. Also, when a turning device with these simple prior art configurations is used, the nut and the turning device quite easily slip during tightening and lossening of the nut, and thus is very difficult to operate.
The aim of this design is to provide an anti-theft device for an automobile wheel which can completely solve the problems mentioned above.